This invention relates to portable barbecue grills, and addresses the problem of reducing the amount of heat that is transferred from the floor of a portable grill to the substrate upon which it rests. More specifically, the invention discloses a heat shield that rests between the burner and floor of the grill, reflecting much of the radiant heat upwards toward the food grid.
Portable cooking grills have become very popular as outdoor cooking devices, generally burning pressurized gas from a burner or charcoal on a grate as the heat source. When preparing for cooking, the grill is placed on a substrate, such as a picnic table, and the heat source is ignited. Heat will radiate downward from the heat source, as well as upward, causing heating of the floor and lower walls of the grill body. The substrate will also become hot due to both conduction and radiation of heat from the floor of the grill. During cooking, the temperature of the substrate can reach upwards of 130xc2x0 F. to 140xc2x0 F. above the ambient temperature.
Standards proposed by the American Gas Association (xe2x80x9cAGAxe2x80x9d) and the Canadian Standards Association (xe2x80x9cCSAxe2x80x9d) require that portable grills heat the substrate surface no more than 90xc2x0 F. above ambient temperature. Meeting this standard involves delicately balancing the design criteria of blocking the heat flow, while permitting sufficient airflow for supporting combustion.
It is therefore an object of this invention to provide an improved heat shield for a portable grill that minimizes heat transfer to the substrate surface.
It is still another object of this invention to provide an improved heat shield for a portable grill that meets the AGA standard, providing sufficient air flow to promote efficient combustion.
It is yet another object of this invention to provide an improved heat shield for a portable grill that features a construction intended to minimize warping during use.
These and other objects are met or exceeded by the present invention which features a heat shield to deflect radiant heat upward away from the floor of the grill. The present shield also acts as a heat sink, allowing heat to be dissipated by the intake air entering the grill under the heat shield, and flowing upwards around the shield to reach the heat source for combustion.
More specifically, the present invention provides a portable gas grill that rests on a substrate. The grill includes a grill body having a floor, a burner and a heat shield including a substantially planar main portion and having at least one elongate, covered air channel. The heat shield is positioned between the burner and the floor to minimize heat transmission to the substrate. Spacing of the shield above the floor allows better air circulation through vent holes in the floor of the grill. Airflow to the burner is maintained through the heat shield, preferably through the use of an air channel that aligns with the vent holes on the floor of the grill body.
Use of this heat shield reflects heat away from the floor of the grill, thus minimizing the temperature increase of the substrate due to conduction and radiation of heat from the floor of the grill. The shield also acts as a heat sink, absorbing heat from the heat source and dispersing it to the surroundings while minimizing the amount of heat that is transferred to the grill floor. When the grill floor is cooler, it is less likely to damage the substrate due to heat.
This invention also meets the AGA standards for both substrate temperature rise and carbon monoxide levels. Support of the heat shield off the surface of the grill floor, as well as the air channel design, maximizes air flow through the air channels, keeping carbon monoxide levels very low. This feature also allows the maximum dissipation of heat from the shield in other directions. As fresh combustion air at ambient temperature enters the grill from the vent holes under the shield, the air contacts the shield, transferring heat to the air by conduction and convection. Passing by the burner, the temperature of the air is increased further, making it much lighter than the incoming combustion air. The hot air then passes by or circulates around the food. Upon removal of the grill lid, the hot air escapes from the grill. Thus, heat from the shield is eventually released to the atmosphere by convection due to the airflow pattern around the heat shield, and radiation from other portions of the grill body.